The impact of severe plastic deformations obtained by hydrostatic extrusion on the machinability of ultrafine-grained Ti grade 2 intended for fasteners.

Abstract The study aimed to examine the effect of severe plastic deformation (SPD) using the hydrostatic extrusion (HE) method on the machinability of grade 2 titanium in the turning process. An analysis of the deformation process was carried out involving a two-stage process of cold hydrostatic extrusion with cumulative true strain ɛ = 2.28. After the deformation, the Ti grade 2 microstructure was strongly defected and significantly refined, resulting in a clear increase in the mechanical properties, UTS strength by 190%, YS yield strength by 230%, and hardness by 50%. The average grain size was 100 nm. Ti grade 2 in the initial state and after HE hydrostatic extrusion process was subjected to machining by turning analysis. Component cutting forces were analyzed at cutting depths a p = 0.3 mm and 0.5 mm, the variables were cutting speed V c and feed rate f . The cutting speeds for the materials in the initial state and after the HE process were 20, 30, and 50 m/min, and the feed rates were 0.08 and 0.13 m/s. Application tests of screws made of Ti grade 2 after HE were also carried out. The tests included the analysis of the surface roughness and the verification of the dimensional tolerance of the pitch diameter d2 required by standards for commercial screws.